poc for widget delete

[michelson]

This is a proof of concept for Widget Deletion.
it assumes a custom configuration where handleDelete option is provided for the widget. This test adds a debugger on the callback for testing purposes. I've to think about the design for this implementation on how will be configured. But the main idea is to check on del or backspace event for widgets that handle deletion and execute it's callback.
The callback function provides the editor context and the current block which is deleted.

handleDelete(ctx, block){
     var url = block.toJS().data.url
     // do your ajax DELETE 
},

issue ref: #23